EXPRESSION OF THE ARABIDOPSIS ABI1-1 MUTANT ALLELE INHIBITS PROTEINASE-INHIBITOR WOUND-INDUCTION IN TOMATO

Abscisic acid (ABA) is an essential component in the wound signalling cascade. Increased levels of endogenous ABA were observed after woundi ng and shown to be a requisite for wound-induced expression of the pro teinase inhibitor II genes. We have taken advantage of the dominant ch aracter of the Arabidopsis abi1-1 mutation, to investigate whether ABI 1 has a function in ABA signalling in response to wounding. Transgenic tomato plants carrying copies of either the wild-type ABI1 or the mut ant abi1-1 alleles were obtained and assayed for wound-induction of th e pin2 or LAP genes. While normal levels of gene induction were observ ed in the transgenic ABI1 plants, the abi1-1 transformants displayed a severe wilty phenotype and reduced seed dormancy. Expression of the a bi1-1 dominant mutation blocked accumulation of the drought-induced TA S14 and LE25 mRNAs in response to ABA, as well as ABA- and wound-induc ed expression of the defense-associated pint and LAP transcripts. MeJA -induction of the pin2 and LAP mRNAs, on the contrary, was not affecte d in the abi1-1 transformants. These results indicate that abi1-1 inhi bits wound-induced expression of the pint and LAP transcripts by block ing ABA-induction of these genes. This implicates ABI1 in wound-signal ling and suggests that a common early ABA signalling pathway may funct ion in the responses to wounding and water stress.